INFLUENCE OF THE CONDITION OF THE SURFACE.
By very careful rubbing of such a polished, steel sphere, it was found possible to increase the height of fall to 162·5 cm. (well over 5 feet) and yet to secure a perfectly "airless," "smooth" splash. But the equilibrium of the splash, if I may use the phrase, is, at this high velocity of entry (564 cm. per sec., or about 18 feet per sec.), very unstable, and was found to depend on minute differences in the condition of the surface. How minute this difference may be, which yet makes the whole difference in the character of the splash, may be gathered from the following extract from the original paper:—
SERIES XII
Smooth sphere of polished serpentine falling 100 centim. into water. Scale 3/4.
| 1 T = 0 |
| 2 0·001 sec. |
| 3 0·002 sec. |
"A polished steel sphere 15·9 cm. in diameter was found (by naked-eye observation) to give an airless splash when falling into water from a height of 132·5 cm.; at 137·5 cm., there was much air taken down. This observation at 137·5 cm. was repeated three times, observer C. doing the polishing. Then observer W. polished, and the splash was first nearly airless and then quite airless. Then, by persevering in the rubbing, the height of fall was gradually raised to 162·5 cm., and a perfectly airless splash was secured, and even at 172·5 cm. the record was 'very little air indeed.'
"Again, a polished marble sphere 2·57 cm. in diameter falling into water from a height of 112 cm. was found to take down 'much air' when rubbed with a certain clean handkerchief A, and 'none at all, or only very little,' when rubbed with clean handkerchief B. This result was confirmed four times with B and five with A. These handkerchiefs were subsequently examined under the microscope, but were found to be extremely similar, and the cause of the difference remained for the time beyond conjecture.